Pressure sensor encapsulated in elastomeric material, and system including the pressure sensor

ABSTRACT

A packaged pressure sensor, comprising: a MEMS pressure-sensor chip; and an encapsulating layer of elastomeric material, in particular PDMS, which extends over the MEMS pressure-sensor chip and forms a means for transferring a force, applied on a surface thereof, towards the MEMS pressure-sensor chip.

BACKGROUND Technical Field

The present disclosure relates to a packaged pressure sensor, to anassembly including the packaged pressure sensor, to a system includingthe packaged pressure sensor and to a method of making the packagedpressure sensor.

Semiconductor pressure sensors operate by detecting a pressure acting ona thin membrane, or diaphragm, of silicon suspended over a semiconductorbody. Assembly of the semiconductor body and of the membrane defines acavity for deflection of the membrane when a force acts thereon.

Currently, sensors are known that are able to measure high pressurevalues and are provided with a core of stainless steel, fixed on whichare strain-gauge elements. The strain-gauge elements detect thegeometrical deformation of the core to which they are associated byvariations of electrical resistance. However, these sensors, for reasonsof reliability, size, and costs are not very convenient to use inautomotive applications. Furthermore, they do not provide highprecision.

There are likewise known integrated pressure sensors, obtained with thesemiconductor technology. These sensors typically comprise a thinmembrane, or diaphragm, suspended over a cavity provided in a siliconbody. Formed within the membrane are piezoresistive elements connectedtogether to form a Wheatstone bridge. When subjected to a pressure, themembrane undergoes deformation, causing a variation of resistance of thepiezoresistive elements, and thus an unbalancing of the Wheatstonebridge. As an alternative, capacitive sensors are available, where themembrane provides a first plate of a capacitor, whereas a second plateis provided by a fixed reference. During use, deflection of the membranegenerates a variation of the capacitance of the capacitor, which may bedetected and associated to the pressure exerted on the membrane.

However, these semiconductor sensors may not in themselves be used formeasuring high pressures in so far as they typically have low full-scalevalues. Thus, for high-pressure applications, an appropriate packagingis to be provided for the aforesaid semiconductor pressure sensors. Forinstance, materials used for the packaging include steel, stainlesssteel, ceramic. In particular, some pressure sensors are arranged incontainers of ceramic or steel having a base area much larger than thesensitive area of the semiconductor pressure sensor. Then, thesecontainers are filled with oil for ensuring an extensive surface forapplication of the force to be measured and a uniform distribution ofthe force itself. However, use of oil requires the container to befluid-tight and, in addition to involving high costs, limits the fieldof application thereof.

BRIEF SUMMARY

Embodiments described herein are directed a packaged pressure sensor, anassembly including the packaged pressure sensor, a system including thepackaged pressure sensor and a method of making the packaged pressuresensor.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the disclosure, some embodiments thereofwill now be described, purely by way of non-limiting example and withreference to the attached drawings, wherein:

FIG. 1 is a cross-sectional view of a packaged pressure sensor accordingto an aspect of the present disclosure;

FIG. 2 is a partially exploded perspective view of the packaged pressuresensor of FIG. 1;

FIGS. 3 and 4 are cross-sectional views of respective packaged pressuresensors according to respective embodiments of the present disclosure;

FIG. 5 is a cross-sectional view of a packaged pressure sensor accordingto another aspect of the present disclosure;

FIG. 6 is a cross-sectional view of a packaged pressure sensor accordingto a further aspect of the present disclosure;

FIGS. 7-9 are cross-sectional views regarding steps for manufacturing apackaged pressure sensor according to a further embodiment of thepresent disclosure;

FIG. 10A is a cross-sectional view of an embodiment of a packagedpressure sensor provided according to the steps of FIGS. 7-9;

FIG. 10B is a cross-sectional view of an alternative embodiment of apackaged pressure sensor provided according to the steps of FIGS. 7-9;

FIG. 11 shows the packaged pressure sensor of FIG. 10A or 10B, which ismounted on a printed-circuit board (PCB) and may be used as pushbutton;

FIG. 12 is a block diagram for an electronic device comprising a packagepressure sensor according to one aspect of the present disclosure; and

FIG. 13 shows a cross-sectional view of an electronic device housing apackaged pressure sensor according to an embodiment of the presentdisclosure.

DETAILED DESCRIPTION

FIG. 1 shows, in lateral section in a plane of coordinates X, Y, Z, apackaged pressure sensor 1, according to an embodiment of the presentdisclosure. In the following description, the term “pressure sensor”should be intended to encompass also the term “force sensor”, being theforce and the pressure related by the formula P=F/A (i.e., pressure isforce F divided by area A), or equivalently F=P·A. The terms “pressuresensor” and “force sensor” may therefore be used in an interchangeableway.

FIG. 2 is a partially exploded perspective view of the packaged pressuresensor of FIG. 1.

The pressure sensor 1 comprises a container 2 having a bottom wall 2 aand one or more lateral walls 2 b (in FIG. 2, one singlecircularly-shaped lateral wall 2 b is shown). The lateral walls 2 b andthe bottom wall 2 a may be a monolithic structure (as shown in FIG. 1)or alternatively a plurality of isolated components coupled together.The lateral walls 2 b have a top surface 2 b′ whose extension is definedby the thickness of the lateral walls 2 b. A cavity 4 extends in thecontainer 2, inferiorly delimited by an internal side 4 a of the bottomwall 2 a and laterally delimited by internal sides 4 b of the lateralwalls 2 b. The top surface 2 b′ of the lateral walls 2 b lies parallelto the XY plane and, in a top view, surrounds the cavity 4.

A sensor chip 6, e.g. including micromachined sensing elements, ishoused in the cavity 4.

The container 2 may be of any suitable material, such as steel,stainless steel, ceramic, or metal alloys with low coefficient ofthermal expansion (e.g., iron alloys with nickel and cobalt, thechemistry of which is controlled for presenting characteristics of lowand uniform thermal expansion).In greater detail, the sensor chip 6 iscoupled to the internal side 4 a of the bottom wall 2 a of the container2, either directly or by further elements therebetween as illustrated inFIG. 1 and described in what follows. The sensor chip 6 is of a per seknown type, and includes an application specific integrated circuit(ASIC) 6′, mounted on which is a pressure sensor 6″ formed usingmicro-electro-mechanical system (MEMS) technology, and is hereinreferred to as a MEMS sensor 6″.

The MEMS sensor 6″ and the ASIC 6′ may be electrically coupled in anyknown manner, for example through conductive wires (wire bonding), orsolder balls, or any other suitable means.

The MEMS sensor 6″ of the sensor chip 6 includes, in particular, asemiconductor body 6 a (e.g., silicon) defining a cavity 6 b suspendedover which is a membrane (or diaphragm) 6 c, which is also, for example,of silicon. The membrane 6 c is typically obtained with micromachiningsteps that include photolithographic and of wet-etching or dry-etchingprocesses. The membrane 6 c is configured to deflect towards the cavity6 b under the action of a force that acts thereon. In or on the membrane6 c one or more piezoresistive elements (not illustrated in the figure)are formed, for example four piezoresistors may be connected together toform a Wheatstone bridge. When subjected to pressure, the membrane 6 cundergoes deformation, causing a variation of resistance of thepiezoresistive elements and thus an unbalancing of the Wheatstonebridge, which may be measured and correlated to the value of pressureacting on the MEMS sensor. The piezoresistive elements are, inparticular, arranged at the vertices of an ideal cross centered at thecenter of the membrane 6 c, and constituted regions with a doping of a Ptype. The piezoresistive elements may be obtained via diffusion ofdopant atoms through an appropriate diffusion mask, and have, forexample, an approximately rectangular cross-section. As an alternativeto the Wheatstone-bridge connection, the piezoresistive detectionelements may form part of a ring oscillator circuit.

According to a different embodiment, the sensor chip 6 operatescapacitively as is well known in the art. In this case, nopiezoresistive elements are present.

Generally described the ASIC 6′ is semiconductor die includes one ormore electrical components, such as integrated circuits. Thesemiconductor die is made from a semiconductor material, such assilicon, and includes an active surface in which integrated circuits areformed. The integrated circuits may be analog or digital circuitsimplemented as active devices, passive devices, conductive layers, anddielectric layers formed within the semiconductor die and electricallyinterconnected according to the electrical design and function of thesemiconductor die. The ASIC 6′ is configured to communicate with theMEMS sensor 6″ by sending signals thereto and receiving signalstherefrom.

The sensor chip 6 is coupled, through the ASIC, to a printed-circuitboard (PCB) 8 by a coupling region 10, for example formed by an adhesivetape, such as a thin film of polyimide, or otherwise by solderingregions. In the case of use of an adhesive film, the ASIC 6′ iselectrically coupled to the PCB 8 with one or more conductive wires 7.The sensor chip 6 and the PCB 8 are thus stacked on top of one another.The PCB 8 lies on the bottom 4 a of the internal cavity 4 of thecontainer 2, and is coupled to the bottom 4 a by a layer of glue or ofan adhesive tape, or layers of temperature-stable polyamide.

The PCB 8 may be one of a flexible PCB, a rigid PCB, an epoxy PCB, aceramic PCB, or even else, according to the needs.

It is noted that, according to an aspect of the present disclosure, aninterface element, such as an organic substrate, or a ceramic substrate,provided with solder pads (for example a BGA—“Ball Grid Array”) may bearranged between the ASIC 6′ and the PCB 8. In this case, the ASIC 6′ iscoupled to the BGA and the BGA is coupled to the PCB 8. The interfaceelement is not explicitly shown in the drawings. The ASIC integrates thefunctions of conditioning of the analog signal with amplification anddigitization for offering a digital interface that is robust againstdisturbance. The PCB 8 integrates the functions of mechanical supportand of interface and routing for the electrical connections.

A polydimethylsiloxane (PDMS) filling layer 12 completely fills theinternal cavity 4, surrounding the sensor chip 6 and the PCB 8. Thefilling layer 12 extends in contact with the membrane 6 c of the sensorchip 6, but not in the internal cavity 6 b, which is insulated so as notto jeopardize the functions of the sensor chip 6. PDMS may be replacedby another elastomeric material, such as for example generic siliconerubbers, polymeric elastomers, silicone gels. In the sequel of thepresent description, explicit reference will be made to PDMS, withoutthis implying any loss of generality.

The container 2 further comprises a covering cap 14, configured to bedirectly or indirectly coupled to the top surface 2 b′ of the lateralwalls 2 a so as to delimit the cavity 4 at the top. Therefore, whenmounted, the covering cap 14 closes the cavity 4, and, when the cavity 4is filled with the filling layer 12, it is in direct contact with saidfilling layer 12.

According to one embodiment, the internal cavity 4 has a volumecomprised between 10⁻⁶ m³ and 10·10⁻⁶ m³, for example 2·10⁻⁶ m³. More inparticular, the aforesaid volume is defined by an area of the internalside 4 a of the bottom wall 2 a, lying in the plane XY, of a valuecomprised between 10⁻⁵ m² and 10⁻³ m², for example 3·10⁻⁴ m², andlateral walls 2 b having a main extension, along Z, of a value comprisedbetween 1 mm and 20 mm, for example 5 mm. The cap 14 has a base area ofa value comprised between 10⁻⁵ m² and 10⁻³ m², for example 3·10⁻⁴ m²,and a thickness, measured along Z, equal to one millimeter or a fewmillimeters, for example between 1 mm and 5 mm, in particular between 1mm and 2 mm, for example 1.5 mm.

PDMS is introduced into the internal cavity 4, in liquid form and in theabsence of gas bubbles and is then made to solidify, in a per se knownmanner, for example during a curing step at high temperature, e.g., atleast 100° C. for some minutes (e.g., 10-20 min).

In order to ensure complete filling of the cavity 4 and at the same timea contact between the cap 14 and the filling layer 12, it is preferableto fill the internal cavity 4 after mounting of the cap 14, through anappropriate hole made through the container 2. Given the viscosity ofPDMS and the subsequent step of solidification thereof, the presentapplicant has found that there are no problems of significant exit, orspread, of PDMS out from the hole used for its introduction.Furthermore, said hole may be plugged or soldered in a per se knownmanner.

During use, when a pressure, or force, is applied on the cap 14 (in thedirection of the arrow 16 in FIG. 1), any deflection of the cap 14 inthe direction Z is transferred to the filling layer 12, which in turntransfers the pressure to the membrane 6 c of the sensor chip 6, whichfunctions as transducer, converting the deflection undergone by themembrane 6 c into a electrical signal processed by the ASIC 6′ andsupplied to the PCB 8. The force applied on the packaged pressure sensor1 is thus detected by the sensor chip 6. The packaged pressure sensor 1is able to measure forces, applied in the direction indicated by thearrow 16, in the range 0.1-100 kN.

The present applicant has found that PDMS is designed to transfer theforce applied to the cap 14 with high directionality and is thus suitedto the application in the context described.

The cap 14 further offers a surface of application of the force 16 thatis more extensive than that offered by the membrane 6 c of the sensorchip 6 and more uniform than that offered by the PDMS layer in theabsence of the cap 14. In use, thus, the cap 14 acts as pressuredemultiplier, increasing the area of application of the force, andrendering it uniform.

As has been said, PDMS, when subject to compression, propagates theforce applied thereto with good directionality along the line of actionof the force. Thus, a sensor chip 6 arranged along the line of action ofthe force applied is subject to a force greater than a sensor chiparranged laterally with respect to the line of action of the force.Likewise, what has been said applies to a sensor chip 6 arranged in theproximity of the cap 14, which will be subject to a force of intensitygreater than a sensor chip arranged in the proximity of the bottom ofthe container 2.

In this regard, as illustrated in FIG. 3, which shows a packagedpressure sensor 1′ according to a further embodiment, it is possible toshape the internal cavity 4 of the container 2 for presenting first andsecond resting regions 18, 19, where the first resting region extends inthe plane XY to a height h₁, measured along Z starting from the bottom 4a of the cavity 4, greater than the height h₂ to which the secondresting region 19 extends. In any case, the values of h₁ and h₂ aresmaller than the maximum depth h_(TOT), along Z, of the cavity 4. By wayof example, the value of h_(TOT) is chosen between 1 mm and 20 mm, forexample 5 mm; the value of h₁ is chosen between 1 mm and 20 mm, forexample 15 mm; the value of h₂ between 1 mm and 5 mm, for example 1 mm.The second resting region 19 may, in one embodiment, coincide with theinternal side 4 a of the bottom wall 2 a.

Each first and second resting region 18, 19 houses a respective sensorchip 20, 21 coupled to a respective PCB 23, 25. Each sensor chip 20, 21is similar to the sensor chip 6 (it comprises, that is, an ASIC 20′, 21′and a MEMS 20″, 21″) and thus is not described further herein in theinterest of brevity.

According to a further embodiment, illustrated in FIG. 4, a packagedpressure sensor 1″ comprises a cap 24 shaped for having thicknesses t₁,t₂ different from one another (in particular, t₁ smaller than t₂) in thefirst resting region 18 and second resting region 19, respectively. Inthis way, in use, when a force of pressure acts on the cap 24 fromoutside, a thin region 24 a, having a thickness t₁, of the cap 24 willundergo a deflection greater than a thick region 24 b thereof, having athickness t₂. Consequently, transmission of this pressure to the PDMSlayer 4 will be more accentuated in the thin region 24 a of the cap 24than in the thicker regions 24 b thereof.

For instance, the thin region 24 a of the cap 24 has a thickness t₁,measured along Z, comprised between 1 and 5 mm, in particular between 2and 3 mm; the thick region 24 b has a thickness t₂, measured along Z,greater than that of the thin region 24 a, for example greater by oneorder of magnitude (between 10 and 50 mm), in particular between 20 and30 mm.

With reference to both of the embodiments of FIGS. 3 and 4, both of thesensor chips 20 and 21 detect, in use, a pressure variation generated bythe variation in temperature of the filling layer 12, which expands andis compressed as a function of the operating temperature. The signalgenerated by each sensor chip on account of the variation of temperatureis a noise signal that adds to the useful signal represented by thevariation of pressure due to the external force to be detected. In thecase of FIGS. 3 and 4, however, the sensor chip 21 is minimally subjectto the pressure generated by the external force to be detected, for thereasons set forth above. It may thus be used as reference for monitoringthe temperature-noise signal, which may be subtracted, by an appropriateprocessing system external to the pressure sensor 1′, 1″, from thepressure signal supplied by the sensor chip 20.

Irrespective of whether the embodiment of FIG. 1, FIG. 3, or FIG. 4 isconsidered, each sensor chip contained in the cavity 4 communicates withthe respective PCB 8, 23, or 25 on which it is mounted, and said PCB 8,23, 25 communicates with the outside of the packaged pressure sensor bya respective hole 26 (in FIG. 1) or holes 27 (in FIGS. 3 and 4) madethrough the container 2, through which there pass one or more electricalwires, designated as a whole by the reference 28. The one or moreelectrical wires are in direct electrical contact with the sensor chip 6and/or with the PCB 8, and/or in electrical contact with the sensor chip6 via the PCB 8. The hole 26 or holes 27, in the respective embodiments,have a diameter of a size such as to enable passage of the electricalwires 28 but not exit of PDMS in liquid form during filling of thecavity 4. In any case, since PDMS is viscous, any exit thereof insignificant amounts is unlikely; further, since it is solidifiedimmediately after it has been poured, any possible exit thereof does notjeopardize proper operation of the packaged pressure sensor.

According to a further aspect of the present disclosure, the PCB 8 maybe a flexible PCB. In this case, at least one of the electrical wires 28may a portion of the flexible PCB 8 extending through the container 2.

It is evident that the container 2, like the internal cavity 4, may bemodeled according to the need, on the basis of the specific applicationof use of the packaged pressure sensor. The container 2, and/or thecavity 4, may consequently have a quadrangular or generically polygonalshape, a toroidal shape, or any other shape. Further, it is evident thatit may house any number of sensor chips. Furthermore, in the case wherea plurality of sensor chips are present in the cavity 4, they may sharea same PCB, for example using a flexible circuit board (FCB) that may bemodeled for respecting the internal conformation of the cavity 4.

FIG. 5 shows a further embodiment of a packaged pressure sensor 29according to a further aspect of the present disclosure. Elements of thepressure sensor 29 which are the same as elements of the pressure sensor1 are indicated with the same reference numerals and not furtherdescribed in detail. In particular, it is noted that the interfaceelement (e.g., a BGA) between the ASIC 6′ and the PCB 8, disclosed withreference to FIG. 1, may be present also in the embodiment of FIG. 5,even if not explicitly shown in the drawing.

The pressure sensor 29 comprises the container 2, in particular made ofceramic material. However, the container 2 may also be of stainlesssteel or metal alloys such as iron alloys with nickel and cobalt (e.g.,the chemistry of which is controlled for presenting characteristics oflow and uniform thermal expansion). The container 2 defines the internalcavity 4, where the sensor chip 6 is housed. The sensor chip 6 iscoupled to the internal side 4 a of the bottom wall 2 a of the container2 in the internal cavity 4, either directly or by further elementstherebetween as illustrated in FIG. 5 and already described in FIG. 1.The sensor chip 6 is of a per se known type, and includes theapplication specific integrated circuit (ASIC) 6′, mounted on which is apressure sensor obtained using micro-electromechanical sensor (MEMS)technology 6″, referred to herein as a MEMS sensor 6″. The sensor chip 6may operate capacitively or piezoresistively.

The sensor chip 6 is coupled, through the ASIC 6′, to theprinted-circuit board 8 by the coupling region 10, for example formed byan adhesive tape, such as a thin film of polyimide, or otherwise bysoldering regions. In an embodiment, the ASIC integrates the functionsof conditioning of the analog signal with amplification and digitizationfor offering a digital interface that is robust against disturbance,while the PCB 8 integrates the functions of mechanical support and ofinterface and routing for the electrical connections.

A polydimethylsiloxane (PDMS) filling layer 31 (analogous to the fillinglayer 12 previously discussed) completely fills the internal cavity 4,surrounding the sensor chip 6 and the PCB 8. The filling layer 31extends in contact with the membrane 6 c of the sensor chip 6, but notin the internal cavity 6 b, which is insulated so as not to jeopardizethe functions of the sensor chip 6. PDMS may be replaced by anotherelastomeric material, such as for example generic silicone rubbers,polymeric elastomers, silicone gels. In the sequel of the presentdescription, explicit reference will be made to PDMS, without thisimplying any loss of generality.

In the embodiment of FIG. 5 a covering cap, such as the covering cap 14of FIGS. 1 and 3, is not present. Instead, the filling layer 31 extendsat a height, along Z direction, which is at least the same as theheight, along Z direction, of the lateral walls of the container 2.Preferably, the filling layer 31 extends at a height which is higherthan that of the lateral walls 2 b of the container 2. Accordingly, thecavity 4 is not delimited, nor covered, at its top, and the fillinglayer 31 is directly exposed to the environment.

As shown in FIG. 5, according to an embodiment of the presentdisclosure, the filling layer 31 has a curved, or convex, profile; inother words, a top surface 31 a of the filling layer may have adome-like shape whose central portion 31 a′ effectively extends at aheight which is higher, along Z, than that of peripheral portions 31 a″of the filling layer 31; more in particular, according to the embodimentof FIG. 5, the filling layer 31 has a height, at peripheral portions 31a″ adjacent to the lateral walls 2 b of the container 2, which is aboutthe same as that of the lateral walls 2 b of the container 2. Therefore,according to this embodiment, the filling layer 31 does not cover thetop surface 2 b′ of the lateral walls 2 b.

FIG. 6 shows a further embodiment of a packaged pressure sensor 33according to a further aspect of the present disclosure. Elements of thepressure sensor 33 which are common to the pressure sensor 1 and/or thepressure sensor 29 are identified using the same reference numerals, andnot further described.

In the pressure sensor 33, the filling layer 31 extends at least in parton the top surface 2 b′ of the lateral walls 2 b. In particular, thefilling layer 31 extends on the top surface 2 b′ of the lateral walls 2b in such a way to completely cover the top surface 2 b′.

In this case, the top surface of the filling layer 31 may have a curved,or convex, profile (dome-like top surface 31 a); or alternatively thefilling layer 31 may be modeled (e.g., through a cutting step) so as tohave a planar or substantially planar top surface 31 a.

With reference to both FIG. 5 and FIG. 6, during use, a pressure, orforce, is directly applied to the filling layer 31 (i.e., on at least asuperficial portion of the top surface 31 a), in the direction of thearrow 16 in FIGS. 5, 6.

Any deflection of the filling layer 31 in the direction Z is transferredto the membrane 6 c of the sensor chip 6, which functions as transducer,converting the deflection undergone by the membrane 6 c into anelectrical signal processed by the ASIC 6′ and supplied to the PCB 8.The force applied on the filling layer 31 is thus detected by the sensorchip 6. The pressure sensor 29 and the pressure sensor 33 are able tomeasure forces, applied in the direction indicated by the arrow 16, inthe range 1-100 N.

The teaching put forward with reference to FIGS. 5 and 6 may be likewiseapplied to the embodiments of FIGS. 3 and 4. In this case, the packagedpressure sensors 1′ do not include the cap 14 and 24 and the fillinglayer is directly exposed to the force, or pressure, applied to it.

FIGS. 10A and 10B show respective further embodiments of a packagedpressure sensor 30, according to further aspects of the presentdisclosure. FIGS. 7-9 show steps for manufacturing the packaged pressuresensor 30 of FIGS. 10A and 10B. Elements of the packaged pressure sensor30 that are common to the above described packaged pressure sensors,such as the packaged pressure sensor 1, are designated by the samereference numerals.

In this case, the packaged pressure sensor 30 is the same in structureand function as the packaged pressure sensor 1 of FIGS. 1 and 2, or thepackaged pressure sensor 29 of FIG. 5, or the packaged pressure sensor33 of FIG. 6; however, the pressure sensor 30 of FIGS. 10A and 10B doesnot have any container 2 or a cap 14. Rather, the outer surface of thepackage is provided by an encapsulating layer 32, in particular ofelastomeric material, which may be any one of the examples providedabove in reference to filling layer 12 of FIGS. 1 and 2, or fillinglayer 31 of FIGS. 5 and 6. In an exemplary embodiment, disclosed in thefollowing, encapsulating layer 32 is of PDMS.

For manufacture of the packaged pressure sensor 30, a sensor chip 6 isused that includes an ASIC 6′ and a MEMS pressure sensor 6″ of the typealready described with reference to FIG. 1. The MEMS sensor is, forinstance, of a membrane type, which is exposed and in direct contactwith the encapsulating layer 32.

For manufacture of the packaged pressure sensor 30 of FIGS. 10A and 10B,reference is now made to FIGS. 7-9. With reference to FIG. 7, the stackformed by the ASIC 6′ and by the MEMS 6″ (hereinafter, sensor chip 6) isarranged in a temporary container 34, for example of polycarbonate,Teflon, or steel. To prevent, during the subsequent manufacturing steps,the sensor chip 6 from moving from its position, an adhesive tape 38 maybe used for keeping it glued to the bottom of the temporary container34.

In reference to FIG. 8, PDMS in liquid form and without gas bubbles ispoured into the temporary container 34, in a way similar to what hasbeen described with reference to FIG. 1 for covering the sensor chip 6evenly. A curing step enables solidification of the PDMS to form afilling layer 39 that covers the sensor chip 6 completely.

In reference to FIG. 9, a step of cutting of the temporary container andof the PDMS is carried out along cutting planes parallel to the planesXZ and YZ. By way of example, illustrated in FIG. 9 are cutting lines40. In this way, the side walls of the temporary container 34 areeliminated. For instance, the cutting planes XZ and YZ are aligned tothe perimeter of the ASIC 6′. There is thus formed the encapsulatinglayer 32 of FIG. 10A.

It is noted that, as a direct consequence of the manufacturing process,a top surface 32 a of the encapsulating layer 32 may not besubstantially flat; instead, it may have an irregular profile, or acurved profile, or a convex profile. The filling layer 39 may likewisebe cut on top, i.e., parallel to the plane XY, to reduce its thickness,if desired, and/or to flatten the top surface 32 a. There is thus formedthe encapsulating layer 32′ of FIG. 10B.

The bottom wall of the temporary container and the layer of adhesivetape are then removed, to obtain the packaged pressure sensor 30 ofFIGS. 10A and 10B.

The thickness, along Z, of the PDMS layer is between 0.1 mm and 5 mm,for example 1 mm.

The packaged pressure sensor 30 may be mounted, for example, on a PCB 42and located in a device for application as pushbutton, as illustrated inFIG. 11, which may be used in a weighing machine, an aid fortouchscreens to evaluate the intensity of the pressing force, a sole fora smart shoe, of silicone material, equipped with integrated pressuresensors, and other applications still.

Furthermore, the packaged pressure sensor 30 may likewise be used forproviding buttons in electronic devices, such as cellphones, wearabledevices, etc. Such an electronic device 300 is shown in FIG. 12, whichincludes a controller 310 and a packaged pressure sensor assembly 312,which may include any of the packaged pressure sensors described herein,such as the packaged pressure sensor 10 of FIG. 1, or the packagedpressure sensor 29 of FIG. 5 or the packaged pressure sensor 33 of FIG.6, or the packaged pressure sensor 30 of FIG. 8A or 8B. The packagedpressure sensor assembly 312 is electrically coupled to the controller.The controller 310 includes control circuitry, which may include one ormore processors, memory, and discrete logic. The controller 310 isconfigured to transmit signal to and receive signals from the pressuresensor assembly 312. As mentioned above, the pressure sensor assembly312 may be part of an input/output device of the electronic device, suchas part of a push button for the electronic device. The electronicdevice may further include a power supply 314, which may be a battery orcomponents for coupling to an external power source.

FIG. 13 shows, in a cross-sectional view, a portion of an electronicdevice 320 provided with a plurality of packaged pressure sensors 312according to an embodiment of the present disclosure, in particular thepackaged pressure sensor 30 of FIG. 10B. It is apparent that theembodiments of the packaged pressure sensor 29 of FIG. 5, of thepackaged pressure sensor 33 of FIG. 6, and/or of the packaged pressuresensor 30 of FIG. 10A may be used as well. The electronic device 320 isin particular a cellphone or smartphone, but it can be any otherelectronic device provided with a touch screen, such as a tablet, apersonal computer, an audio player, a wearable device (e.g. a smartwatch) and the like. According to further embodiments, the electronicdevice 320 may be a track-pad, a pointing device (e.g., a touch mouse)or a keyboard (e.g., a touch keyboard. The electronic device 320 mayeven be part of a smart-pen which can be used to write or draw on asmartphone or tablet. In this case, the electronic device 320 isintegrated in the point of the smart pen.

The electronic device 320 comprises a bottom cover 321, which forms asupporting base for a PCB 322, in a per se known manner. The electronicdevice 320 further comprises a top cover 324 which forms, or includes, ascreen of the electronic device 320, typically made of glass. The topcover 324 and the bottom cover 321 are mechanically coupled to oneanother through coupling elements 323, including, but not limited to,screws, glue, mating connectors or fasteners, or any other suitablecoupling elements. The top cover 324 and the bottom cover 321 define,when coupled, an inner space 326. In an embodiment, the top cover 324and the bottom cover 321 lie on parallel planes.

A touch-sensitive modulus 328 (adapted to sense a touch of a user of theelectronic device 320) is housed within the inner space 326, adjacent tothe top cover 324. The touch-sensitive modulus 328 is of a per se knowntype (e.g., it implements a capacitive touch screen) and thus will notbe described in detail in the interest of brevity.

Packaged pressure sensors 312, for example four packaged pressuresensor, are located laterally to the touch-sensitive modulus 328,between the PCB 322 and the top cover 324, within the inner space 326.The packaged pressure sensors 312 may be located at the four corners ofa rectangular-shaped electronic device 320. In general, the packagedpressure sensors 312 may be in any number other than four, and arrangedat other locations of the electronic device 320 between the PCB 322 andthe top cover 324, spaced apart from the touch-sensitive modulus 328.

More in detail, each packaged pressure sensors 312 is coupled to the PCB322 through a respective solder region 330, formed between conductivebottom leads of the ASIC 6′ and respective conductive lines of the PCB322. Each packaged pressure sensors 312 extends towards the top cover324. In an embodiment of the present disclosure, each packaged pressuresensors 312 is in direct contact with the top cover 324 through theencapsulating layer 32. In another embodiment of the present disclosure,not shown, each packaged pressure sensors 312 may be in contact with thetop cover 324 through one or more intermediate layers or spacingelements. The latter solution may be useful in case the packagedpressure sensors 312 are manufactured with an extension, along the Zdirection, equal to, or lower than, the thickness, along the Zdirection, of the touch-sensitive modulus 328.

During use, a pressure applied on the top cover 324 and directed, atleast in part, along Z direction, causes a compression of theencapsulating layer 32 of one or more packaged pressure sensors 312(depending on the region of the top cover 324 of applied pressure). Theencapsulating layer 32 transfers the pressure to the membrane 6 c of therespective sensor chip 6, which functions as transducer, converting thedeflection undergone by the membrane 6 c into a electrical signalprocessed by the ASIC 6′. Each packaged pressure sensors 312 which issubject to the applied force, therefore, generates an electrical signalindicative of the applied pressure and transfers such electrical signalto the PCB 322, for further processing. In particular, the pressure thussensed and transduced may be used to provide the electronic device 320with the further functionality of a pressure-sensitive screen, i.e., theelectronic device 320 is not only responsive to the touch of the user inthe XY plane (functionality provided by the touch-sensitive modulus 328)but it is also sensitive to the pressure applied by the user on thescreen along Z direction. The processing details of the electricalsignals supplied by each packaged pressure sensors 312 to the PCB 322are not part of the present disclosure and therefore not furtherdescribed.

From what has been described above, various advantages of the disclosureillustrated emerge clearly in the various embodiments.

In particular, embodiments of the present disclosure are simple toproduce, presents reduced costs, and enables a wide versatility ofpractical application.

Finally, it is evident that modifications and variations may be made tothe disclosure described, without departing from the scope of thepresent disclosure. In particular, the dimensions and the embodimentsmay vary with respect to what has been described for adapting the sensorto the specific scope.

The various embodiments described above can be combined to providefurther embodiments. For example, the teachings of FIGS. 3 and 4 may becombined with the teachings of FIGS. 7-9 and 10A, 10B. In this case, thepackaged pressure sensor 30 may include a supporting substrate wherein afirst MEMS pressure-sensor chip is coupled on a first supporting region,and a second MEMS pressure-sensor chip is coupled on a second supportingregion, the first and second supporting regions lying on differentplanes.

The pressure sensor according to each of the previously disclosedembodiments may be used to sense a pressure, or force, which isuniformly applied on it, as well as a punctual pressure or force appliedto a certain (restricted) area of the cap or of the elastomericencapsulating layer, according to the respective embodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

The invention claimed is:
 1. A method of making a sensor package, the method comprising: placing a pressure sensor die in a container; filling the container with a flowable elastomeric material such that the flowable elastomeric material covers the pressure sensor die; hardening the elastomeric material; and after hardening the elastomeric material, removing the container thereby exposing at least one surface of the elastomeric material.
 2. The method according claim 1, further comprising the step of flattening a top surface of the hardened elastomeric material.
 3. The method according to claim 1, wherein: the container is a closed container with a first opening and a second opening; a conductive element extends through the first opening; and the flowable elastomeric material is provided through the second opening to fill at least the portion of the container.
 4. The method according to claim 3, wherein filling at least the portion of the container with a flowable elastomeric material comprising completely filling the container.
 5. A method, comprising: placing a pressure sensor die in a container, the pressure sensor die including a membrane or a diaphragm, wherein the container is a closed container with a first opening and a second opening, wherein a conductive element extends through the first opening; completely filling the container with a flowable elastomeric material that covers the pressure sensor die; hardening the elastomeric material, wherein the hardened elastomeric material is configured to transfer a force to the membrane or the diaphragm of the pressure sensor; and cutting through the hardened elastomeric material to form a package.
 6. The method according to claim 5, wherein the substrate is an application specific integrated circuit (ASIC) die.
 7. The method according to claim 6, wherein the ASIC die and the pressure sensor are coupled to a support.
 8. The method according to claim 7, wherein cutting through the hardened elastomeric material comprises cutting through the support.
 9. The method according to claim 5, further comprising coupling the package to a printed circuit board.
 10. The method according to claim 5, wherein the flowable elastomeric material is polydimethylsiloxane.
 11. A method, comprising: stacking a pressure sensor die and application specific integrated circuit (ASIC) die relative to each other in a container to form a stacked device, the pressure sensor die including a membrane or a diaphragm, wherein the container is a closed container with a first opening and a second opening, a conductive element extending through the first opening; covering the pressure sensor die with a flowable elastomeric material, wherein the covering includes providing the flowable elastomeric material through the second opening to fill at least the portion of the container; and hardening the elastomeric material, wherein the hardened elastomeric material is configured to transfer a force to the membrane or the diaphragm of the pressure sensor.
 12. The method according to claim 11, wherein before covering the pressure sensor die with the flowable elastomeric material includes placing the stacked device into a container, wherein covering the pressure sensor die includes introducing the flowable elastomeric material into the container, the method further comprising removing the container.
 13. The method according to claim 11, wherein the flowable elastomeric material is polydimethylsiloxane.
 14. The method according to claim 11, further comprising cutting through the hardened elastomeric material to form a package.
 15. The method according to claim 14, wherein covering the pressure sensor die with a flowable elastomeric material comprises placing the stacked pressure sensor die and the ASIC die on the support in a container and introducing the flowable elastomeric material into the container and over the pressure sensor.
 16. The method according to claim 15, wherein cutting through the hardened elastomeric material includes cutting through the support.
 17. The method according to claim 14, comprising coupling the package to a printed circuit board. 